Where do they mount up at.

I bolted through the stock bumper mounts. Works great.

 

I hope that gives you an idea

LOL while retaining the factory bumper please.

on this one, I think I just had 1 really long bolt on each side that went through the bumper (styrofoam filled) and through a stock hole in the bumper back plate (thin sheetmetal) with large washers to hold it in place because the stock holes were large...

 

it wasn't done to take heavy abuse, but my friend Russ who has had this wagon for the last 4-5 years, takes it offroading to go to some of his favorite fishing holes, and has never had a problem with it...